THIS IS A SHANNON AWARD PROVIDING PARTIAL SUPPORT FOR THE RESEARCH PROJECTS THAT FALL SHORT OF THE ASSIGNED INSTITUTE'S FUNDING RANGE BUT ARE IN THE MARGIN OF EXCELLENCE. THE SHANNON AWARD IS INTENDED TO PROVIDE SUPPORT TO TEST THE FEASIBILITY OF THE APPROACH; DEVELOP FURTHER TESTS AND REFINE RESEARCH TECHNIQUES; PERFORM SECONDARY ANALYSIS OF AVAILABLE DATA SETS; OR CONDUCT DISCRETE PROJECTS THAT CAN DEMONSTRATE THE PI'S RESEARCH CAPABILITIES OR LEAD ADDITIONAL WEIGHT TO AN ALREADY MERITORIOUS APPLICATION. THE APPLICATION BELOW IS TAKEN FROM THE ORIGINAL DOCUMENT SUBMITTED BY THE PRINCIPAL INVESTIGATOR. Amphetamine (AMPH) and cocaine are self-administered drug long implicated in refractory social and clinical problems. Progress in approaches to psychostimulant abuse is restricted by limited understanding of how the drugs alter neurotransmission. Our long-range goal is to elucidate mechanisms by which psycho-stimulants alter neurotransmission and to determine how these actions initiate downstream effects. The weak base model of AMPH action, in which vesicular dopamine (DA) is redistributed to the cytosol by collapse of the vesicular electrochemical gradient followed by DA release by reverse transport through the uptake carrier, suggests mechanisms that may explain important effects on neurotransmission. We will address the action of these drugs on synaptic neurotransmission and the initiation of methAMPH neurotoxicity. 1. We will elucidate mechanisms by which AMPH and cocaine alter DA release by exocytosis. Psycho-stimulant studies generally focus on alterations of extrasynaptic DA levels that apparently mediate reward. A corollary of the weak base model is that there should be a reduction in the amount of transmitter released per vesicle exocytosis (i.e., reduced quantal size) that would inhibit synaptic neurotransmission. Using electrochemical techniques, we have found that AMPH and cocaine reduce the quantal size of vesicular release, apparently via different mechanisms. These actions may underlie other psychostimulant-induced responses such as sensitization, craving, withdrawal, and psychosis. 2. A prediction of our model is that increased cytosolic DA would promote cellular release by reverse transport. We will elucidate the kinetics and ion dependence of DA release by reverse transport and its regulation by AMPH and neuronal depolarization. 3. We will examine steps that underlie AMPH-mediated neurotoxicity in neuronal culture. MethAMPH neurotoxicity in midbrain cultures is similar in important ways to that seen in vivo but is technically more tractable. A prediction from our results is that methAMPH-induced process degeneration is initiated by redistribution of DA from the reducing environment of the vesicle to the relatively oxidizing cytosol in varicosities. We will establish if intracellular oxidation mediates process degeneration and inhibits mitochondrial respiration.